From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Subject: Re: [PATCH v4 2/2] mm/gup/writeback: add callbacks for inaccessible pages References: <20200306132537.783769-1-imbrenda@linux.ibm.com> <20200306132537.783769-3-imbrenda@linux.ibm.com> <3ae46945-0c7b-03cd-700a-a6fe8003c6ab@intel.com> <20200415221754.GM2483@worktop.programming.kicks-ass.net> <20200416141547.29be5ea0@p-imbrenda> <20200416165900.68bd4dba@p-imbrenda> <20200416183431.7216e1d1@p-imbrenda> From: Dave Hansen Message-ID: <396a4ece-ec66-d023-2c7e-f09f84b358bc@intel.com> Date: Thu, 16 Apr 2020 12:02:54 -0700 MIME-Version: 1.0 In-Reply-To: <20200416183431.7216e1d1@p-imbrenda> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: To: Claudio Imbrenda Cc: Peter Zijlstra , Andy Lutomirski , linux-next@vger.kernel.org, akpm@linux-foundation.org, jack@suse.cz, kirill@shutemov.name, "Edgecombe, Rick P" , Sean Christopherson , borntraeger@de.ibm.com, david@redhat.com, aarcange@redhat.com, linux-mm@kvack.org, frankja@linux.ibm.com, sfr@canb.auug.org.au, jhubbard@nvidia.com, linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org, Will Deacon , "Williams, Dan J" On 4/16/20 9:34 AM, Claudio Imbrenda wrote: >> Ahh, so this is *just* intended to precede I/O done on the page, when >> a non-host entity is touching the memory? > yep OK, so we've got to do an action that precedes *all* I/O to a page. That's not too bad. I still don't understand how this could work generally, though There are lots of places where I/O is done to a page without either going through __test_set_page_writeback() or gup() with FOLL_PIN set. sendfile() is probably the best example of this: fd = open("/normal/ext4/file", O_RDONLY); sendfile(socket_fd, fd, &off, count); There's no gup in sight since the file doesn't have an address and it's not being written to so there's no writeback. How does sendfile work?